As mobile communication technology develops, traditional voice communication services can not satisfy communication demand, and people have urgent demand for experiencing new multimedia services. The multimedia services include not only simple audio and video communication services but also instant messaging, stream media services, etc., especially services that combine new communication manner and traditional voice communication.
As the trend of combination of Internet and telecom networks, 3GPP (The 3rd Generation Partnership Project) has introduced the IMS (IP Multimedia Subsystem) of full IP service network architecture which supports multimedia services based on the Packet Bearer Network. The IMS depends on customized user data to keep independent of user access modes, to control openness of service capability, and to provide new multimedia communication experience.
FIG. 1 is a schematic diagram of the IMS entities and interfaces defined by 3GPP. The main function entities in IMS are CSCF (Call Session Control Function) and HSS (Home User Server).
CSCF are in three types: S-CSCF (Serving-Call Session Control Function), P-CSCF (Proxy-Call Session Control Function), and I-CSCF (Interrogating-Call Session Control Function). The P-CSCF is the first contact point for UE (User Equipment) in the IMS. The P-CSCF performs Proxy function, receives SIP (Session Initiation Protocol) messages and performs corresponding process, then forwards it. The I-CSCF is mainly designed to interrogate and to perform functions of network topology hiding. When the user registers, the I-CSCF queries from the HSS and determines the S-CSCF which serving for the user. The S-CSCF records the call state of the user and performs call control function. The S-CSCF is the main service control entity. Different S-CSCFs may perform different service functions by connecting different ASes (application servers).
The HSS stores user information and service data for each IMS user, and communicates with the CSCFs to perform routing function and roaming function; meanwhile, the HSS provides authentication, authorization, IMSI/IP address mapping, locating function, etc. The user information includes: user number and address information, security information for authentication and authorization, location information for supporting the user to register, user locations information in different systems and user profile etc. The service data includes service triggering rules, service triggering logic, etc.